[72.03] Implications of Early Galactic Be and B on Cosmic Ray Origin

R. Ramaty (NASA - GSFC), R. E. Lingenfelter (UCSD - CASS)

Atomic spectroscopic measurements of Be abundances in old
halo stars formed in the early Galaxy can provide
information on the origin of the cosmic rays. A major source
of all the light elements (Li, Be and B) is cosmic ray
spallation, with Be almost certainly being produced solely
by cosmic rays. The measured abundance ratio, Be/Fe, as a
function of the metallicity (i.e. Fe/H) of the stars in
which the abundances are measured is essentially constant,
independent of metallicity for Fe/H from 10^-3 to about
10^-1 of the solar value. Fe production in this epoch is
dominated by core-collapse supernovae, with the IMF averaged
Fe yield per supernova essentially independent of
metallicity. This constancy, coupled with the observed
constant Be/Fe, requires a constant Be production per
core-collapse supernova (within a factor of \sim2). If the
cosmic rays were accelerated only out of the ISM, then their
composition would evolve proportionally to that of the ISM,
and the Be yield per supernova would increase with
metallicity because of the increase in the C and O
abundances of both the ISM and the cosmic rays. Moreover, Be
production by cosmic rays accelerated out of the ISM would
also be energetically untenable, requiring about 10^53
erg in cosmic rays per supernova at the lowest
metallicities. Thus, the acceleration of all the cosmic rays
in the early Galaxy out of the ISM is inconsistent with the
Be data, implying that the cosmic rays (or at least the C
and O) are accelerated out of freshly synthesized matter
before it mixes into the ISM. We shall discuss the
limitations of this conclusion and its implication on the
origin of the current epoch cosmic rays.

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